Re: [PATCH] c++ modules: verify_type failure with typedef enum [PR106848]

[Patrick Palka <ppalka@redhat.com>]

On Wed, 19 Oct 2022, Richard Biener wrote:

> On Tue, Oct 18, 2022 at 8:26 PM Patrick Palka <ppalka@redhat.com> wrote:
> >
> > On Fri, 14 Oct 2022, Richard Biener wrote:
> >
> > > On Thu, Oct 13, 2022 at 5:40 PM Patrick Palka via Gcc-patches
> > > <gcc-patches@gcc.gnu.org> wrote:
> > > >
> > > > Here during stream in we end up having created a type variant for the enum
> > > > before we read the enum's definition, and thus the variant inherited stale
> > > > TYPE_VALUES and TYPE_MIN/MAX_VALUES, which leads to an ICE (with -g).  The
> > > > stale variant got created from set_underlying_type during earlier stream in
> > > > of the (redundant) typedef for the enum.
> > > >
> > > > This patch works around this by setting TYPE_VALUES and TYPE_MIN/MAX_VALUES
> > > > for all variants when reading in an enum definition.  Does this look like
> > > > the right approach?  Or perhaps we need to arrange that we read the enum
> > > > definition before reading in the typedef decl?  Note that seems to be an
> > > > issue only when the typedef name and enum names are the same (thus the
> > > > typedef is redundant), otherwise we seem to read the enum definition first
> > > > as desired.
> > > >
> > > >         PR c++/106848
> > > >
> > > > gcc/cp/ChangeLog:
> > > >
> > > >         * module.cc (trees_in::read_enum_def): Set the TYPE_VALUES,
> > > >         TYPE_MIN_VALUE and TYPE_MAX_VALUE of all type variants.
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > >         * g++.dg/modules/enum-9_a.H: New test.
> > > >         * g++.dg/modules/enum-9_b.C: New test.
> > > > ---
> > > >  gcc/cp/module.cc                        | 9 ++++++---
> > > >  gcc/testsuite/g++.dg/modules/enum-9_a.H | 5 +++++
> > > >  gcc/testsuite/g++.dg/modules/enum-9_b.C | 6 ++++++
> > > >  3 files changed, 17 insertions(+), 3 deletions(-)
> > > >  create mode 100644 gcc/testsuite/g++.dg/modules/enum-9_a.H
> > > >  create mode 100644 gcc/testsuite/g++.dg/modules/enum-9_b.C
> > > >
> > > > diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> > > > index 7ffeefa7c1f..97fb80bcd44 100644
> > > > --- a/gcc/cp/module.cc
> > > > +++ b/gcc/cp/module.cc
> > > > @@ -12303,9 +12303,12 @@ trees_in::read_enum_def (tree defn, tree maybe_template)
> > > >
> > > >    if (installing)
> > > >      {
> > > > -      TYPE_VALUES (type) = values;
> > > > -      TYPE_MIN_VALUE (type) = min;
> > > > -      TYPE_MAX_VALUE (type) = max;
> > > > +      for (tree t = type; t; t = TYPE_NEXT_VARIANT (t))
> > > > +       {
> > > > +         TYPE_VALUES (t) = values;
> > > > +         TYPE_MIN_VALUE (t) = min;
> > > > +         TYPE_MAX_VALUE (t) = max;
> > > > +       }
> > >
> > > it's definitely somewhat ugly but at least type_hash_canon doesn't hash
> > > these for ENUMERAL_TYPE (but it does compare them!  which in principle
> > > means it could as well hash them ...)
> > >
> > > I think that if you read both from the same module that you should arrange
> > > to read what you refer to first?  But maybe that's not the actual issue here.
> >
> > *nod* reading in the enum before reading in the typedef seems like
> > the most direct solution, though not sure how to accomplish that :/
> 
> For LTO streaming we DFS walk tree edges from all entries into the tree
> graph we want to stream, collecting and streaming SCCs.  Not sure if
> doing similar for module streaming would help this case though.

FWIW I managed to obtain a more interesting reduction for this ICE, one
that doesn't use a typedef bound to the same name as the enum:

$ cat 106848_a.H
template<typename _T1>
struct pair {
  using type = void(*)(const _T1&);
};
struct _ScannerBase {
  enum _TokenT { _S_token_anychar };
  pair<_TokenT> _M_token_tbl;
};

$ cat 106848_b.C
import "106848_a.H";

using type = _ScannerBase;

$ g++ -fmodules-ts -g 106848_a.H 106848_b.C
106848_b.C:3:14: error: type variant differs by TYPE_MAX_VALUE
<enumeral_type 0x7f252c757f18 _TokenT ...>
<enumeral_type 0x7f252c757f18 _TokenT ...>

Like in the less interesting testcase, the problem is ultimately that we
create a variant of the enum (as part of reading in pair<_TokenT>::type)
before reading the enum's definition, thus the variant inherits stale
TYPE_MIN/MAX_VALUE.

Perhaps pair<_TokenT>::type should indirectly depend on the definition
of _TokenT -- but IIUC we generally don't require a type to be defined
in order to refer to it, so enforcing such a dependency would be a
pessimization I think.

So ISTM this isn't a dependency issue (pair<_TokenT>::type already
implicitly depends on the ENUMERAL_TYPE, just not also the enum's
defining TYPE_DECL), and the true issue is that we're streaming
TYPE_MIN/MAX_VALUE only as part of an enum's definition, which the
linked patch fixes.

> 
> > A somewhat orthogonal issue (that incidentally fixes this testcase) is
> > that we stream TYPE_MIN/MAX_VALUE only for enums with a definition, but
> > the frontend sets these fields even for opaque enums.  If we make sure
> > to stream these fields for all ENUMERAL_TYPEs, then we won't have to
> > worry about these fields being stale for variants that may have been
> > created before reading in the enum definition (their TYPE_VALUES field
> > will still be stale I guess, but verify_type doesn't worry about that
> > it seems, so we avoid the ICE).
> >
> > patch to that effect is at
> > https://gcc.gnu.org/pipermail/gcc-patches/2022-October/603831.html
> >
> > >
> > > Richard.
> > >
> > > >
> > > >        rest_of_type_compilation (type, DECL_NAMESPACE_SCOPE_P (defn));
> > > >      }
> > > > diff --git a/gcc/testsuite/g++.dg/modules/enum-9_a.H b/gcc/testsuite/g++.dg/modules/enum-9_a.H
> > > > new file mode 100644
> > > > index 00000000000..fb7d10ad3b6
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/g++.dg/modules/enum-9_a.H
> > > > @@ -0,0 +1,5 @@
> > > > +// PR c++/106848
> > > > +// { dg-additional-options -fmodule-header }
> > > > +// { dg-module-cmi {} }
> > > > +
> > > > +typedef enum memory_order { memory_order_seq_cst } memory_order;
> > > > diff --git a/gcc/testsuite/g++.dg/modules/enum-9_b.C b/gcc/testsuite/g++.dg/modules/enum-9_b.C
> > > > new file mode 100644
> > > > index 00000000000..63e81675d0a
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/g++.dg/modules/enum-9_b.C
> > > > @@ -0,0 +1,6 @@
> > > > +// PR c++/106848
> > > > +// { dg-additional-options "-fmodules-ts -g" }
> > > > +
> > > > +import "enum-9_a.H";
> > > > +
> > > > +memory_order x = memory_order_seq_cst;
> > > > --
> > > > 2.38.0.68.ge85701b4af
> > > >
> > >
> > >
> >
> 
>